ANNIVERSARY ADDRESS OF THE PRESIDENT. 93 



In the operculate land-shells the evidence is clearer. Of the 

 Cydosto7natidce, the genus Cydotopsis is peculiar to the Mascarene 

 Islands and the peninsula of India, and affords a case somewhat 

 similar to that of Etroplus in the freshwater fishes, the only other 

 members of the family found in the Oriental region being an Otopoma, 

 met with in Cutch, and Realia {Omphcdotropis) *, another Mascarene 

 genus, in the Andaman and Nicobar Islands and some of the Malay 

 islands t. But Otopoma is also found in Southern Arabia, Socotra, 

 &c., and does not penetrate India further east than Catch ; whilst 

 Realia is an insular type, probably possessing peculiar faculties for 

 migration, and ranges through various islands to Polynesia and 

 Kew Zealand. It is reasonable to suppose that, in whatever way 

 the transfer may have taken place, Cydotopsis reached India from 

 the Mascarene Islands, where Cydostomatidce abound. On the 

 other hand, there are found on the Seychelles Cyaihopoma, a 

 genus chiefly developed in Peninsular India, Leptopoma, a Malay 

 type, found also in Ceylon, and ffelidna, not found in India or Ceylon, 

 but occurring in Eurma and ranging throughout the Malay Archi- 

 pelago and Polynesia to America and the Antilles. These types, 

 belonging to two totally distinct families, Cydophoridce and Helici- 

 nidce, must apparently have reached the Seychelles from the east- 

 ward, for not one of them is found in Africa. Now if there was 

 not land-connexion between India and the Seychelles, these mollusks 

 must have been transported either by floating objects, a means of 

 migration concerning which I have already expressed grave scepti- 

 cism, or through the air. But anything floating would be transported 

 from the Seychelles to the Indian coasts, never the reverse, as is 

 shown by the Seychelles double cocoanut, or cocos de me?', having 

 been known long before its origin was discovered through being 

 occasionally thrown upon the Maldives and Sumatra. I have 

 examined the weather-charts of the Arabian Sea and neighbouring 

 portions of the Indian Ocean, on which the currents for different 

 periods of the year ure shown, and I think it is evident that the 

 westwardly currents which prevail in parts of the sea from. November 



* Many of the shells referred to Oynphalotropis in works on land-moUiisca 

 really belong to Assiminea, a brackish-water form belonging to a different 

 family. 



t The peculiar Madagascar shell called Acroptychla metahleta is wonderfully 

 like Cydophoms foliace us ivom the Nicobar Islands, and C. Leai from the Anda- 

 mans. The Madagascar Mascaria is represented in Ceylon by Cataulus, in the 

 Himalayas, Burma, and Borneo by Coptochilm, and in the Neotropical region 

 by Megalomastoma. 



